Mononuclear phagocytes orchestrate the innate immune response through the combinatorial interplay between the phagocytic uptake and killing of bacterial invaders, clearance of apoptotic cells, antigen presentation, and secretion of vesicle bound signaling molecules to recruit help in the clearance of infection. Central to each of these functions is the activation of ion channels and transporter proteins that drive function in intracellular compartments. Chloride channels as well as proton translocating ATPases prime the phagosomal compartment for effective bactericidal activity, and secretory vesicles for mobilization and release. Dynamic changes in intraphagosomal pH, Cl- content, and membrane potential are essential to the development of an optimal bactericidal phagosomal lumen. The driving force for changes in ionic content in the small intraphagosomal volume is relatively unknown and likely to be highly dynamic. This proposal will explore the interdependence of phagosomal pH and the identity, regulation, and activation of ion channels present in the phagosomal membrane. Ion channel activity and the resultant changes in phagosomal content are prime determinants of the antimicrobial milieu within the phagosome and, therefore, are prime candidates for new therapeutic targets. We will explore unique regulatory signal transduction pathways to modulate ion channel trafficking/expressing in the phagosome to optimize killing of ingested organisms. The goal of the experiments proposed in this application is the optimization of dynamic functional profiles for monitoring changes in the ionic milieu of th macrophage phagosome during formation and maturation, defining mechanistically the molecular components contributing to the process. These proposed studies will address the question of whether monovalent and divalent cation flux can replace non-functional Cl- channels in driving bactericidal activity; and if so, how the appropriate channels can be recruited to the phagosome. We will determine the spatiotemporal regulation of the ionic movements and the transporter elements which can fine tune and maintain the microbicidal environment. In toto, these studies will provide both methodology and a template for the exploration of novel mechanisms which might resolve inflammation in a host-directed manner in a diversity of pulmonary diseases including tuberculosis, chronic pulmonary obstructive disease (COPD), cystic fibrosis (CF) and asthma. They also will provide a roadmap that could be helpful for the study of other intracellular organelles in a wide range of cell biological contexts and disease states.